Chronology

The geological history
of Shetland spans over half of the Earth's history. Although no rocks remain on
land that are younger than the Devonian (~380 Myr), the
oldest rocks on Shetland, the Lewisian of North Roe, reach back
to almost 3000 Myr.

Our understanding is poor of the timing of the major events that have shaped
the present land surface of Shetland. This uncertainty reflects the fact that Shetland has been an
area of net erosion for much of the last 60 million years. The
general sequence of events on Shetland can be pieced
together using evidence from sediments in the North Sea (Johnson et al,
1993) and the continental shelf west of Shetland (Stoker et al, 1993).

We can view the landscape history of Shetland in terms of three main periods,
each much shorter than its precursor:

the Tertiary (65-2.5 Myr) saw the shaping of the main preglacial features
of the terrain, the major hills and valleys